Hydrocephalus is a neurological condition caused by the abnormal accumulation of cerebrospinal fluid (CSF) within the ventricles, or cavities, of the brain. Hydrocephalus, which can affect infants, children and adults, arises when the normal drainage of CSF in the brain is blocked in some way. Such blockage can be caused by a number of factors, including, for example, genetic predisposition, intraventricular or intracranial hemorrhage, infections such as meningitis, or head trauma. Blockage of the flow of CSF consequently creates an imbalance between the rate at which CSF is produced by the ventricular system and the rate at which CSF is absorbed into the bloodstream. This imbalance increases pressure on the brain and causes the ventricles to enlarge. Left untreated, hydrocephalus can result in serious medical conditions, including subdural hematoma, compression of the brain tissue, and impaired blood flow.
Hydrocephalus is most often treated by surgically inserting a shunt system to divert the flow of CSF from the ventricle to another area of the body, such as the right atrium, the peritoneum, or other locations in the body where CSF can be absorbed as part of the circulatory system. Various shunt systems have been developed for the treatment of hydrocephalus. Typically, shunt systems include a ventricular catheter, a shunt valve and a drainage catheter. At one end of the shunt system, the ventricular catheter can have a first end that is inserted through a hole in the skull of a patient, such that the first end resides within the ventricle of a patient, and a second end of the ventricular catheter that is typically coupled to the inlet portion of the shunt valve. The first end of the ventricular catheter can contain multiple holes or pores to allow CSF to enter the shunt system. At the other end of the shunt system, the drainage catheter has a first end that is attached to the outlet portion of the shunt valve and a second end that is configured to allow CSF to exit the shunt system for reabsorption into the bloodstream. Typically, the shunt valve is palpatable by the physician through the patient's skin after implantation. The shunt valves, which can have a variety of configurations, can be designed to allow adjustment of their fluid drainage characteristics after implantation.
It is also important to be able to externally read or verify the setting of the valve. With some adjustable valves, x-ray images are used to determine the current setting of the valve, before and after adjustment. With other adjustable valves, the orientation of a rotor in the valve can be read magnetically, using a magnetic compass-like device positioned above the valve, outside the skin of the patient. In examples, both the adjuster and the indicator are used in conjunction with a locator. The locator tool is used in the process of determining the location of the valve under the skin and subsequently to maintain this established position. The adjuster and the indicator tools engage within the locator tool to perform their function.
The locator can be placed by palpitating the skin of the patient and aligning a cut out of the valve in the base of the locator. Once placed, the shape of the valve indicates the flow direction, from which the orientation of the valve setting is based. Another type of valve can have an additional marker magnet to allow for the magnetic identification of the flow direction, making it unnecessary to palpitate to locate the valve's direction.
However the locator tool is nevertheless required for proper placement and use of the Adjustment tool. A magneto-resistive sensor based indicator tool needs to be zeroed at a distance of at least 10 to 15 cm from the valve in order to take into account the earth magnetic field. Each time the locator's absolute orientation is changed during use, a new zeroing becomes necessary. This is time consuming. Thus, it is desirable that the locator tool can be turned and aligned with the valve's flow direction whilst maintaining the indicator tool's absolute orientation.